Such a filter is based on the following principles:
utilization of the modes of the screened dielectric resonator; and PA1 reutilization of conventional excitation methods and mode coupling methods, in particular by means of adjustment screws acting on the electric field. PA1 the position of the resonator inside the metal cavity; PA1 the materials used for the cavity, for the adjustment devices, and for the system holding the resonator; and PA1 the principle whereby the dielectric resonator is held inside the cavity. PA1 utilization of invar and carbon fiber; or PA1 utilization of some other material with the expansion coefficients involved being compensated. PA1 low loss insulating materials in the form of a column or a cushion (foam, polystyrene of PTFE (polytetrafluoroethylene)). PA1 it makes it possible to obtain a sufficiently large frequency difference between the HEM.sub.1,2.DELTA. mode, for example, and the others modes for obtaining a relatively wide band free from parasitic modes; and PA1 it enables filters to be made having a structure which is more than two-mode. PA1 the resonator is held by a system of dished washers resting against the inside wall of the cavity via a small rim at one end and using four lock screws bearing against a conical portion of the top washer. This ensures that the resonator is held in place in sprite of differential expansion. PA1 a first part terminating at a first end in a conical bearing surface and at second end in four bearing surfaces for engaging the resonator; and PA1 a second part having one end engaging the resonator and identical to the first part, and having a simple bearing surface at its other end for bearing against the rim of the cavity. PA1 to optimize the Q-factor (no lossy material in critical zones); and PA1 to obtain a temperature stability coefficient of about 1 ppm/.degree.C. (parts per million per degree centigrade), which can be compensated by using a dielectric resonator having a coefficient of -1 ppm/.degree.C.
An article published in "Electronics Letters", Vol. 16, No. 17, Aug. 14, 1980, pp. 646-647, entitled "Dielectric resonator dual mode filter" by P. Guillon, Y. Garault and J. Farenc describes a screened dielectric resonator which is cylindrical in shape in which a plurality of degenerative modes having identical natural frequencies may propagate. These degenerative modes may be coupled to one another in order to for form coupled circuits by disturbing the geometrical shape of the structure: thus, the frequency of the TE.sub.01p mode may be disturbed by means of a tuning screw, and it is possible to obtain a two-mode dielectric filter using the two perpendicularly polarized HEM.sub.1,2,.DELTA. modes of the resonator.
European patent application No. 0 064 799 describes a ceramic resonator element disposed in a cavity in order to form a composite microwave resonator. Two tuning screws situated along orthogonal axes inside the cavity serve to tune the assembly along these axes to frequencies close to the fundamental resonance frequency of the resonator element. A plurality of cavities of this type may be assembled together to form a filter by using a plurality of transverse separations.
The coupling between these various cavities may then be provided by means of single slots, by means of pairs of slots in a cross-configuration, or by means of circular irises. In each cavity an adjustment screw is disposed along an axis at 45.degree. relative to the orthogonal turning screws so that resonance along one of the orthogonal axes is coupled to resonance along the other.
However these prior art documents give no details about:
In other prior art documents, some details are given concerning the materials used for the cavity:
As for the dielectric used for holding, few precise solutions are given, e.g.:
While making it possible to optimize the response curves of dielectric resonator filters in a band close to resonance and over a wide band, the object of the invention is to solve the various questions raised in the making of such filters.